The National Weather Service forecast center in Norman, Oklahoma, is located in a five-story building on the south campus of the University of Oklahoma. It is technically on the second floor, but an auditorium located below it dips partly underground, so the experience is more like being on the first floor. It has a wall of windows facing west and is neither tornado-proof nor tornado-resistant.

“We were conscious that we could be hit,” says Rick Smith, warning coordinator meteorologist, who was on scene Monday from 7 AM through the time the tornado hit at 3 PM. He went home at 11 PM. “We have redundant power systems and plans in place in case we’re affected; we have a back-up center in Tulsa and we practice what we preach about seeking shelter if we have to. We were experiencing power bumps here and there but nothing that took us offline.”

As soon as the day began, it was clear that there would be serious problems. Monday was the third day of a severe stretch of weather that, on Sunday, had already included one EF4 tornado and two deaths. Tornadoes can develop quickly, going from just a puffy white cloud in the sky to an on-the-ground twister in 90 minutes. Yesterday, the storm systems were in place to shrink that window to just an hour. “When I came in the office it became obvious very, very quickly that the conditions were even more volatile than Sunday,” says Smith. It wasn’t just that the weather system was the same as it had been; that would have been bad enough. It was that there also weren’t any counterbalancing atmospheric factors in place that sometimes dampen or prevent the storms. The area was without any natural meteorological defenses.

Despite the turbulence it tracks, the command center is not terribly noisy. “If you were in the room you’d be impressed by the professionalism and quiet,” says Smith. “There’s no shouting, no panic. It’s like being aboard an aircraft carrier, though we didn’t have the colored shirts.”

The room is configured like a command center, with a horseshoe of eight work stations, each with five computer monitors, for a total of 40 screens. Some of those screens are broken up into as many as four panels, so there are many more streams of data coming into each station. There is one large screen at the front of the room displaying a variety of datasets including doppler radar of the weather system itself. There are 9 other screens in that main array carrying feeds from all of the local TV stations as well as from weather helicopters.

That’s not to say the room was completely silent on Monday. The phones were constantly ringing and amateur radio was constantly crackling with reports from professional and volunteer spotters in the field. There was a lot of communication via social media as well, with an on-line weather service chat room frequented by TV stations, emergency response teams and schools. “We were typing information there too, getting ready to issue a warning. The volume we’re pumping out is incredible,” says Smith. They also had a constant presence on Twitter at @NWSNorman. “I don’t know how many thousands of fans and followers we might have picked up yesterday, but if you lost power and phone and TV, it was important that you still have social media.”

Sometime between 2:20 and 2;30 PM, the center issued a severe thunderstorm warning, which meant that tornadoes might be imminent. Given the severity of the conditions, Smith says they were poised to issue both that warning and the tornado emergency warning sooner than they might normally have been. A handful of the meteorologists, including Smith and Andra, were clustered at one of the eight work stations. Andra was the day’s “event coordinator,” making the moment to moment calls. They were all focusing on one of the screens that was showing a radar scan of the entire storm system. Based on the data stream they had coming in, they could overlay a relatively specific threat area on that larger image. The meteorologists knew not just the likely tornado’s intensity but something about its track, so the footprint they drew was both immediate and predictive—at least a little.

The actual warning that the center issued 16 minutes before the twister hit included the rarely used term “tornado emergency.” That designation was created during the devastating May 3, 1999 storms that touched down in Chickasha, Oklahoma, clawed their way through the state and eventually struck Kansas, Arkansas, Texas and Tennessee over the course of three days, claiming 36 lives. It was meteorologist David Andra, who came up with the then-new term. He was part of the Norman team then and is now head of the center. The point of the phrasing was to convey that this was something different from what anyone in the area was likely to have experienced before. “This is not your usual Oklahoma tornado,” says Smith. “This is different; this is deadly.” The term, he says, “wasn’t scientifically studied. It came up in a moment of inspiration, but it was very effective. People understood it. We haven’t used it much since then, but seeing what we saw on TV and knowing what was happening, it was an easy decision to use it again.”

The text for the precise warning (apart from the “tornado emergency” term) is preformatted, so the meteorologists could select, for example, “radar indicates” or “spotters observe.” That takes about 30 seconds to do. They then hit a “generate text” command. The system spits it out, they proofread it and if it’s what they want, they click and send. There is no hotline or red phone; there’s an enter key instead. “This is much improved from when we had to sit down in front of a word processor,” and type it all out, says Smith.

The crew in the Norman office soon knew how terrible the disaster was. TV feeds provided them much the same scenes of devastation that everyone else was seeing, but they couldn’t focus on it fully. They were also tracking storms and issuing warnings across 35 other counties and there had already been tornadoes in the southern part of the state. The day unfolded terribly, but quickly. “It was one of those days when you look up at the clock and it’s 10AM and the next time you look back it’s 6 PM,” says Smith.

Around 7 PM, the team tried to send out for pizza, but the phone lines were down. Someone in the back of the room volunteered to go out to Papa John’s and brought back enough for everybody.